The stereochemistry of tri-n-butyltin hydride reductions in the preparation of ring A desoxygibberellins

Abstract

The hydrogenolysis of gibberellin 1- and 3-chlorides with tri-n-butyltin hydride has been shown by deuterium labelling combined with ¹H and ²H n.m.r. analysis, to proceed with the introduction of the label from the less hindered β-face of the molecule. The hydrogenolysis reaction when applied to the preparation of 3-desoxygibberellins in the C-20 series, proceeds most satisfactorily with the thiocarbonylimidazole derivatives of gibberellins A₁₃ and A₁₄ methyl esters to afford the methyl esters of gibberellins A₂₅ and A₁₂ respectively.